In Bill’s section of the letter, which is addressed to teenagers, the Microsoft founder and billionaire philanthropist argues it should be a development priority to deliver clean energy to the 1.3 billion people who do not have access to power.

He also stresses that the new power needs to be low carbon in order to tackle the risks presented by climate change. “If we really want to help the world’s poorest families, we need to find a way to get them cheap, clean energy,” he writes. “Cheap because everyone must be able to afford it. Clean because it must not emit any carbon dioxide - which is driving climate change.”

And Gates argues the goal has to be truly zero emission power. “Can’t we just aim to cut carbon emissions in half?’ I asked many scientists,” Gates wrote. “But they all agreed that wouldn’t be enough. The problem is that CO2 lingers in the atmosphere for decades. Even if we halted carbon emissions tomorrow, the temperature would still rise because of the carbon that’s already been released. No, we need to get all the way down to zero.”

In something of a break from past comments when Gates has been critical of renewable energy technologies, once dismissing wind and solar power as “cute”, the letter welcomes recent rapid progress on renewable energy.

“New green technologies are allowing the world to produce more carbon-free energy from solar and wind power,” he writes. “Maybe you live near a wind farm or have seen solar panels near your school. It’s great that these are getting cheaper and more people are using them. We should use more of them where it makes sense, like in places where it’s especially sunny or windy. And by installing special new power lines we could make even more use of solar and wind power.”

However, he reiterates his view that to stop climate change and make energy affordable for everyone, the world will need “some new inventions”.

“We need more powerful, more economical solutions,” Gates writes. “In short, we need an energy miracle. When I say “miracle,” I don’t mean something that’s impossible. I’ve seen miracles happen before. The personal computer. The Internet. The polio vaccine. None of them happened by chance. They are the result of research and development and the human capacity to innovate.”

Gates argues that a combination of private sector research and development, such as his recently launched Energy Breakthrough Coalition, government action, and individual endeavour can combine to deliver a new generation of clean energy technologies.

“We need a massive amount of research into thousands of new ideas – even ones that might sound a little crazy – if we want to get to zero emissions by the end of this century,” he said. “New ways to make solar and wind power available to everyone around the clock could be one solution. Some of the crazier inventions I’m excited about are a possible way to use solar energy to produce fuel, much like plants use sunlight to make food for themselves, and batteries the size of swimming pools with huge storage capacity.

“Many of these ideas won’t work, but that’s okay. Each dead end will teach us something useful and keep us moving forward. As Thomas Edison famously said, ‘I have not failed 10,000 times. I’ve successfully found 10,000 ways that will not work’.”

Gates also urged young people to engage with the energy challenge. “You may be wondering what you can do to help,” he wrote. “First, it’s important for everyone to get educated about this energy challenge. Many young people are already actively involved in climate and energy issues and I’m sure they could use more help. Your generation is one of the most globally minded in history, adept at looking at our world’s problems beyond national borders. This will be a valuable asset as we work on global solutions in the decades ahead.

“Second, if you’re someone with some crazy-sounding ideas to solve our energy challenge, the world needs you. Study extra hard in your math and sciences. You might just have the answer.”

“What we need to get that probability [of a breakthrough] up to be very high is to take 12 or so paths to get there,” he told the news agency. “Like carbon capture and sequestration is a path. Nuclear fission is a path. Nuclear fusion is a path. Solar fuels are a path. For every one of those paths, you need about five very diverse groups of scientists who think the other four groups are wrong and crazy.”

He also revealed the Breakthrough Energy Coalition is working on new investment approaches that would provide more “patient capital” than that offered by traditional venture capital funds, allowing for greater investment in long term R&D efforts.